Lactate dehydrogenase (LDH) is a soluble enzyme which is present in the cytosol of a wide variety of organisms. When cells are cultured in vitro, LDH can be released into the culture medium upon the loss of membrane integrity due to cell- or compound-induced cytotoxicity. Since LDH is a stable enzyme, its presence in culture media indicates the loss of cell membrane integrity in response to damage and toxicity. LDH measurement is used to analyze cellular viability and viable cell count, estimate biomass, evaluate the cytotoxicity in cultured cells and determine the health of cells and tissues.
ZellX® LDH Cell Cytotoxicity Colorimetric Assay Kit uses the formazan dye iodonitrotetrazolium (INT) as a colorimetric indicator of enzyme activity. LDH catalyzes the oxidation of lactate to pyruvate via reduction of NAD+ to NADH and H+. The NADH subsequently reduces the INT (yellow) to the highly colored formazan (red) which can be measured at 490 nm.